Liquid level indicating apparatus



Feb. 5, 1952 1 M HlLDYARD 2,584,128

LIQUID LEVEL INDICATING APPARATUS Filed July 3, 1946 Patented Feb. 5, 1952 oFFlcr.

2,584,128 LIQUID LEVEL INDICATTNG APPARATUS Jseph M. nils-yard, United states Army,

. Arlington County, Va.

p f Applicationiiniy, 1946, serial No. 681,274 z claims. (el. 25o-3s) (Granted under the act of March amended April 30, 1928;370 O. G. 757) -The invention described herein may be manufactured and used by or for the Goverment lfor governmental purposes, without the "payment of any royalty thereon.

This invention is in electrical apparatus and more specifically in electronic fluid level controls.

The principal object of this invention is to provide a novel means for determining the level of a fluid in a vessel.

Another object is to provide means for maintaining a desired uid level.

Other objects will be apparent from a reading of the following specification and claims.

In the drawings:

Figure 1 is a diagrammatic illustration of my invention;

Figure 2 is a schematic diagram of the oscillator used in my invention; and

Figure 3 shows a modification of my invention.

Referring to the drawings and particularly to Figure 1, I is a tank containing a fluid Il and having an inlet I2. A pipe I3, closed by a diaphragm I4 at its upper end, is placed in fluid I I. A vent is provided at I5 so that the fluid level in pipe I3 may be the same as the level in vessel ID.

The diaphragm is to be vibrated or exed, and for this purpose there are provided a coil I6, similar to that used in a loudspeaker, a magnet I6' supported adjacent the top Aof the pipe in any convenient fashion, as by brackets I6", and an oscillator I1 (see Figure 2). A meter I8 in the oscillator circuit (calibrated in centimeters, feet, or some similar units) is used to determine the level of fluid II. Valve I9 is provided to draw oli the fluid II through outlet I9'.

With the fluid II closing one end and the diaphragm I4 closing the other end, pipe I3 is a resonant closed pipe. There will be one uid level at which the pipe will be in resonance with a signal from oscillator I1 transmitted to the pipe by diaphragm I4. At resonance, the waves reflected by the surface of fluid I I will be in phase with those transmitted by diaphragm I4 and thus the load presented to the oscillator I1 will be at a minimum. It follows then that any other uid level pipe I3 will be out of resonance with oscillator I1 (its frequency remaining constant) and, therefore, will present a greater load to it than when the pipe and oscillator are in resonance.

Referring to Figure 2, it can be seen that coil I6 is connected to the plate circuit of triode 20,

and thus any reaction presented to it by the reiiected waves directly affects the plate load.

According to the preferred mode of practicing my invention, the normal fluid level of tank Il) is much higher than that required for a state/of resonance between pipe I3 of Figure 1 and oscillator I'I. In practice, the uid level in thetank is raised to the desired point, whereupon potentiometer 22 of bridge circuit 22, 23, 24, and 25 (Figure 2) is adjusted so that points A-and B are at the same potential.

With points A and Bat the same potential, no current iiow will be registered by meter IB, in shunt with resistor 23 and potentiometer 22. A change of potential at either of the points A or B will result in a current iiow through the parallel paths which include meter I8, resistor 24, and potentiometer 22. By noting the direction of pointer deflection of the meter. it can be determined whether the level of the tank is above or 4below that desired. For example, if the fluid level in tank I0 is above the desired point, the loading of the oscillator circuit in Figure 2 will be greater. Since the grid bias of the oscillator diminishes with increased loading, point A thereupon becomes less negative with respect to B and current flows from A through meter I8 to B, causing a deflection of the indicator in one direction. Contrary conditions will, of course, produce an opposite deflection. By properly Calibrating the meter, it can be determined how much above the desired level the liquid is.

Figure 3 illustrates one way in which the apparatus of my invention may be applied to maintain the level of a fluid in a vessel. The structure should be assumed to be identical with that of Figure 1, and, thus, servo system 30 is shown as being substituted for meter I8 of Figure 1, oscillator I1 being identical with the oscillator of Figure 1, and the other elements of Figure l being assumed to be present although not shown in Figure 3. Servo system 3D is, of course, sensitive to the frequency of the output of oscillator I1 and serves to open or close valve 3|, controlling the flow of iluid into the tank through pipe I2.

It will be understood that the diaphragm I4 can be replaced by any of several structures capable of performing the dual functions of transmitting vibrations to the uid surface and receiving vibrations reiiected therefrom (piezoelectric crystals and magnetostrictive elements, for example), and further that driving means other than a coil and magnet can readily be used.

The foregoing description is in specic terms. For the true scope of the invention, reference should be had to the appended claims.

I claim:

1. In an apparatus of the nature described, a pipe extending downwardly into a body of liquid net said second Winding being arranged within the plate circuit of said tube.

2. In an apparatus of the nature described a pipe extending downwardly into a body of liquid and communicating at its lower end therewith,

an oscillator including an electron tube having a plate circuit, a vibrating device within said pipe adjacent the upper end thereof, a magnet-adjacent said vibrating device, an armature operatively related to said vibrating device and partly within the iield of said magnet, a Winding within the eld of said magnet energizable by said oscillator for varying the flux of said magnet to drive said armature and thereby said vibrating device, and a second Winding within the said eld of said magnet said second winding being arranged Within the plate circuit of said tube.

JOSEPH M. HILDYARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,570,781 Ruben Jan. 26, 1926 1,882,395 Pierce Oct. 11, 1932 2,047,974 Lehr et a1 July 21, 1936 2,156,519 Walker May 2, 1939 2,244,484 v Beers June 3, 1941 l 2,323,128 Hare June 29, 1943 2,431,233 Erwin Nov. 18, 1947 2,433,599 Cohen Dec. 30, 1947 2,472,249 De Giers June 7, 1949 Y FOREIGN PATENTS Number Country Date 171,988 i Great Britain Aug. 24, 1922 OTHER REFERENCES A New Method of Gas Anaiysis by R. Gerberth, Industrial and Engineering Chemistry,` December 1923, p. 1277. 

